IFrames that reference another site are not rendered by the PrintToPdf method on Windows.
This can be reproduced with the cefclient example in version 99.2.13 and a simple html file like this:
<html lang="en" xmlns="http://www.w3.org/1999/xhtml"> <head> <meta charset="utf-8" /> <title></title> </head> <body> <h1> Test </h1> <iframe width="560" height="315" src="https://magpcss.org/ceforum/"></iframe> </body> </html>
The iFrame content is rendered completely blank.
If I run the cefclient with the --enable-print-preview flag the behavior is the same in the print preview.
Running with the --disable-site-isolation-trials flag seems to fix the issue.
Printing to pdf in Chrome with the same version (99.0.4844) works (including print preview).
The cef behavior seems to have changed between versions "77.1.3+gf0a1c44+chromium-77.0.3865.90" and "78.3.1+g8819d2e+chromium-78.0.3904.87"